This invention relates to high voltage switching apparatus. More particularly, it is concerned with apparatus for switching rapidly between selected high voltage levels.
Beam penetration cathode ray tubes are well known for use in electronic information displays in order to provide multi-colored display of data. Typically these devices utilize two different phosphors and produce particular colors depending upon the anode voltages employed to accelerate the electron beam which strikes the phosphors. In a typical example the accelerating anode voltages for a four color beam penetration cathode ray tube are 12 kilovolts for yellowish-green, 10 kilovolts for yellow, 8 kilovolts for orange, and 6 kilovolts for red.
The accelerating voltage is obtained by charging and maintaining the charge across a capacitance. It is desirable that apparatus for changing the voltage across the capacitance operate quickly and be capable of operating at a high repetition rate. For example, the electron beam repositioning time of a cathode ray tube typically may be from 5 to 15 microseconds. It is desirable to be able to change voltage levels within this period of time and also to be able to change voltage levels frequently.
Various types of high voltage generators for switching high voltages have been employed in the operation of beam penetration cathode ray tubes. Vacuum tube type apparatus have been used satisfactorily in certain applications, but have the typical disadvantages of vacuum tubes of limited life, high power consumption, and size. Solid state high voltage switching generators heretofore available have been limited to relatively slow switching speeds. The difficulties of withstanding the high voltages employed and of handling the power requirements at the desired switching speeds and frequency have not been satisfactorily overcome with previously available solid state apparatus.